Method and apparatus for removing thimbles from the stubs of an anode

ABSTRACT

An apparatus and method for removing thimbles ( 12 ) from stubs ( 20 ) of an anode yoke which includes the step of advancing a ram ( 20 ) towards each stub with the force applied by the ram against the stub being limited to a preset maximum, and another step of advancing the rams at the same speed to push the stubs through the thimbles.

This application claims the priority of U.S. provisional patentapplication 60/179,720, filed Feb. 1, 2000, which application isincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for removingthimbles from the stubs of anodes, such as anodes used in theelectrolytic smelting of metals such as aluminum.

BACKGROUND OF THE INVENTION

A carbon anode block, used in the electrolytic smelting of metals suchas aluminum, is supported by yoke stubs attached to an anode rod. Asshown in FIG. 1, each yoke stub 10 has a thimble 12 fitted at its end,and the thimbles 12 may be cast within recesses in the carbon anodeblock. During the electrolytic smelting of metals, the carbon anodeblock is consumed. To replace the consumed carbon anode block, the anoderemnants and the thimbles are removed from the anode yoke stubs with amachine known as a thimble press.

A conventional thimble press generally includes a single ram that isused to push the stubs through the thimbles, thereby removing thethimbles from the stubs. In operation, as shown in FIG. 2, a clamp 14 isplaced around each stub 10, with the opening of the clamp 14 smallenough to prevent the thimble 12 attached to the end of the stub 10 frompassing through. The ram 16 then pushes the stubs 10 (and the thimbles12) towards the clamps 14. When a thimble 12 comes in contact with astationary clamp 14, the movement of the thimble 12 is stopped, and themovement of the stub 10 continues, allowing the clamp 14 to stripe thethimble 12 from the end of the stub 10.

One of the disadvantages of conventional thimble presses is that theremoval of the thimbles using a single ram may generate a significantbending moment in the yoke, which may either damage the yoke or shortenits operating life. This occurs when the ends of the stubs are not even(not unusual under normal working conditions) and thus don't come incontact with the cam at the same time. For example, in the caseillustrated in FIG. 2 where the middle stub 10 is longer than the twoside stubs 10, the ram 16 can only push against the middle stub 10, andthe removal of the two side thimbles 12 generates a bending moment ineach of the yoke arms. For example, if 5,000 kg of force is required toremove a thimble and the distance between the middle stub and each ofthe side stubs is 1 meter, the removal of the side thimbles generates abending moment of 5,000 kg-m in each of the yoke arms.

SUMMARY OF THE INVENTION

The method and apparatus embodying the various aspects of the presentinvention overcome the problems associated with conventional thimblepresses.

In accordance with one aspect of the invention, an apparatus forremoving thimbles from stubs of an anode yoke includes a number ofseparate rams and a ram control system. The rams preferably are capableof independent movements, which are controlled by the ram controlsystem. The ram control system has two modes. In the first mode, eachram is advanced towards a stub, and the ram force is limited to a presetmaximum value. When the ram has contacted the stub, the advancement ofthe ram may be stopped because the maximum ram force may be insufficientto move the stub. In the second mode, the rams are advanced at about thesame speed, preferably at the same speed, to push the stubs through thethimbles, thereby removing the thimbles from the stubs. Preferably, theram control system remains in the first mode until each ram has come incontact with a ram and/or until the force applied by each ram againstthe stub has reached the present maximum value.

In accordance with another aspect of the invention, a method forremoving thimbles from stubs of an anode yoke includes the step ofadvancing a ram towards each stub with the force applied by the ramagainst the stub being limited to a preset maximum, and another step ofadvancing the rams at the same speed, preferably at the same speed, topush the stubs through the thimbles, preferably while not limiting theforce applied by each ram to the preset maximum force. In a preferredembodiment, the first step precedes the second step.

The present invention has a number of advantages over conventionalthimble presses. For example, during the removal of the thimbles, apreferred embodiment of the present invention does not generate asufficiently large bending moment in the yoke arms so as to damage theyoke or shorten its operating life. The reason for this advantage isthat in a preferred embodiment of the present invention, a thimble isremoved by pushing primarily against the stub on which the thimble isinstalled. In other words, the force used to remove a thimble isgenerated by the ram which is pushing the stub on which the thimble isinstalled. In conventional thimble presses, a thimble may be removed bypushing against one or more other stubs when the stubs are not even.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of anode rod, anode yoke and thimbles attached to theyoke tubes.

FIG. 2 is an illustration of the operation of a conventional thimblepress.

FIGS. 3A, 3B and 3C illustrate the operation of a thimble press of thepresent invention.

FIG. 4 is a diagram of a hydraulic ram control system of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the presently preferred embodiments of theinvention refers to the accompanying drawings. The description isdirected to and the drawings show exemplary embodiments of theinvention, other embodiments are possible, and changes may be made tothe embodiments described below without departing from the spirit andscope of the invention. The scope of the invention is defined by theappended claims, and the description and drawings are merelyillustrative, not limiting.

As illustrated in FIGS. 3A and 4, an embodiment of the apparatus forremoving thimbles 12 from the stubs 10 of an anode yoke includes aplurality of rams 20 and a ram control system.

The apparatus may include any number of rams, preferably at least asmany as there are stubs. Each ram 20 may be used to push against a stub10, preferably against an end of the stub 10, and may have anyconfiguration suitable for this purpose. The rams 20 can moveindependently with respect to each other. In the illustrated embodiment,each ram 20 has a generally cylindrical configuration, although it mayhave any one of other suitable configurations. Preferably, each ram 20can easily pass through the opening of the thimble 12, allowing the ram20 to push the stub 10 through the thimble 12. In the illustratedembodiment, this means that the diameter of the ram 20 is less than theinner diameter of the thimble 12.

The apparatus may include a plurality of stops, each of which may beused to stop a thimble or hold it stationary while the stub is beingpushed through the thimble. There are a wide variety of devices that canbe used for this purpose. For example, a clamp 14 may be placed aroundthe stub 10 above the thimble 12 as shown in FIG. 3, and can be used tostop the upward movement of the thimble 12 as the ram 20 pushes the stub10 upwards, allowing the thimble 12 to be removed from the stub 10.Preferably, the clamp 14 is sufficient strong so it can withstand theforce generated by the ram 20.

The ram control system is used to control the movement of the rams 20 sothat no substantial stress is generated in the yoke. In a preferredembodiment, the ram control system includes two modes. In the firstmode, the rams 20 are pushed towards the stubs 10, preferably with theforce applied to each ram 20 limited to a maximum value. If a ram 20encounters a resistance that the maximum ram force cannot overcome, theram 20 will preferably stop. For example, if a ram 20 has come incontact with the end of a stub 10 and the maximum ram force is notsufficient to overcome the resistance created by the stub 10, the ram 20may stop with the ram 20 abutting the end of the stub 10. However, evenif one or more rams 20 have stopped, the other rams 20 may continue tomove forward as long as they have not encountered resistance greaterthan the maximum ram force. Preferably, the maximum ram force issufficient large to ensure that the rams 20 will all reach the stubs 10but is not so large as to damage the yoke or shorten its service life.After all the ram forces have reached the maximum value and/or each ram20 has come in contact with a stub 10, as shown in FIG. 3B, the ramcontrol system preferably will enter the second mode.

In the second mode, all the rams 20 preferably will move withsubstantially the same speed. In this mode, the force applied by eachram 20 preferably is not limited to the preset maximum ram forcediscussed in connection with the first mode, allowing the ram 20 to pushthe stub 10 through the thimble 12. Preferably, a stop or the like isused to stop the movement of a thimble 12 and/or hold the thimble 12stationary while the stub 10 is being pushed through the thimble 12, asshown in FIG. 3C.

The ram control system may include another mode that preferably followsthe second mode. In this mode, the rams 20 retract after the thimbles 12have been removed from the stubs 10.

A ram control system of the present invention may be anelectromechanical, hydraulic or pneumatic system. Shown in FIG. 4 is anexample of a hydraulic ram control system. The system includes a numberof hydraulic circuits 30, one for each ram 20. Although the threehydraulic circuits 30 shown in FIG. 4 are identical, they may bedifferent. Each hydraulic circuit 30 includes a piston-cylinderarrangement 32 for driving the ram 20, and a hydraulic pump 42 fordriving the piston-cylinder arrangement 32. Preferably, the hydraulicpumps 42 are arranged in parallel and driven by a single motor 44, suchas an electric motor. With this arrangement, the pumps 42 (and the motor44) will rotate at about the same speed.

Preferably, each hydraulic circuit 30 also includes a mechanism forlimiting the pressure of the circuit 30 to a preset maximum, a featurethat can be used to limit the force applied by the piston-cylinderarrangement 32 to a preset maximum when the ram control system is in thefirst mode. With this arrangement, the maximum ram force is equal to theproduct of the maximum pressure and the effective piston area. In eachof the circuits 30 illustrated in FIG. 4, this mechanism includes apressure reducing valve 46 which opens to allow the hydraulic fluid toescape when the circuit pressure reaches a preset value, thus limitingthe circuit pressure to the preset value. When the ram control system isin the second mode, the pressure reducing valve 46 may be changed to ahigher setting, making the valve function as a safety valve. In theillustrated embodiment, the pressure reducing valve 46 includes a mainpressure relief valve 48 and two pressure relief valves 50, 52 used tocontrol the setting (pilot pressure) of the main pressure relief valve48. The first pilot pressure relief valve 50 is set at the maximumpressure allowed when the ram control system is in the first mode sothat the main pressure relief valve 48 will open when the pressurereaches the maximum pressure, thus limiting the circuit pressure to themaximum pressure. The second pilot pressure relief valve 52 is set at ahigher pressure so that the main pressure relief valve 48 functions as asafety valve when the ram control system is in the second mode. The ramcontrol system exits the first mode and enters the second mode byswitching from the first relief valve 50 to the second relief valve 52.The switch between the first and second relief valves 50, 52 isaccomplished with a four-way, two-position solenoid valve 54.

Alternatively, each hydraulic circuit 30 may use a pressure-controlled,variable displacement pump, instead of a pressure reducing valve, tolimit the circuit pressure to the maximum allowed when the ram controlsystem is in the first mode. The maximum pressure allowed by the pumpcan be adjusted to a higher value when the ram control system is in thesecond mode.

Each hydraulic circuit 30 may also include a pressure sensor 56, such asa pressure switch, which is used to monitor whether the circuit pressurehas reached the maximum pressure. When the pressure sensors 56 indicatethat all circuit pressures have reached the maximum pressure, indicatingall rams 20 have come in contact with a stub 10, then the ram controlsystem may enter the second mode. Alternatively, instead of a pressuresensor, a flow meter may be installed in each hydraulic circuit todetermine whether there is a sufficient fluid flow through the mainrelief valve 48, indicating the main relief valve 48 is open. An openmain relief valve 48 indicates that the circuit pressure has reached themaximum value.

As discussed above, each hydraulic circuit may include another mode, inwhich the rams retract after the thimbles have been removed. There are anumber of ways to implement this. In the embodiment shown in FIG. 4, forexample, a four-way, three-position solenoid valve 58 is provided. Whenthe valve 58 is at the left position 60, the ram control system is inthis third mode, in which the upper chamber 36 of the cylinder 34 isconnected to the pump 42 and the lower chamber 38 connected to thehydraulic fluid tank 78, forcing the piston 40 to retract to its lowerposition. When the valve 58 is at the right position 62, the ram controlsystem is in either the first or the second mode. The normal position ofthe valve is the middle position 64. In case of a system failure, thevalve is returned to the middle position 64, and the one-way checkvalves 66 ensure that the piston 40 (and the ram 20) stays at itsposition.

Each hydraulic circuit may also include a number of auxiliarycomponents. For example, as shown in FIG. 4, each circuit 30 may includea pressure gage 68. Normally the pressure gage 68 is isolated by amanual valve 70 from circuit pressure. A reading can be taken from thepressure gage 68 by pushing the button 72 of the manual valve 70 toconnect the pressure gage 68 to the hydraulic circuit 30. In addition,each hydraulic circuit 30 may include flexible hoses 74, which allow thepiston-cylinder arrangement 32 to move about during operation. Eachhydraulic circuit 30 may also include an air bleed valve 76 which bleedsout air contained in the hydraulic fluid.

In operation, the anode block is first positioned so that its stubs 10are aligned respectively with the rams 20 of the thimble 12 press. Thena clamp 14 is placed around each stub 10 above the thimble 12. The ramcontrol system then advances the ram 20 towards the stubs 10 with theforce applied by each ram 20 limited to the maximum pressure. In theillustrated embodiment, the movement of a ram 20 (and the piston 40) isaccomplished by positioning the three-position valve in the rightposition and supplying the lower chamber 38 of the cylinder 34 withpressured hydraulic fluid supplied by the pump 42. The pressure reducingvalve 46 is set so that the circuit pressure does not exceed the presetmaximum value. When it reaches the stub 10, each ram 20 preferably willstop because the maximum ram force is not sufficient to move the stub10. When all the rams 20 have come in contact with the respective stubs10, as shown in FIG. 3B, the ram control system enters the second mode,and the rams 20 move forward at about the same speed. When each thimble12 is stopped by a clamp 14, the ram 20 pushes the stub 10 through thethimble 12, removing the thimble 12 from the stub 10, as shown in FIG.3C. Then the three-position valve is placed in the left position,placing the ram control system in the third mode. In this mode, thepistons 40 (and the rams 20) retract to their original positions.

What is claimed is:
 1. An apparatus for removing thimbles from stubs ofan anode, the apparatus comprising: a plurality of rams havingindependent movements; and a ram control system including, a first modedesigned to advance each ram towards a stub and the force applied by theram against the stub is limited to a preset maximum force, and a secondmode designed to advance the rams at the same speed to push the stubsthrough the thimbles.
 2. The apparatus of claim 1 further including aplurality of stops, wherein each stop is positioned to stop the movementof one of the thimbles, thereby allowing the ram to push the stubthrough the thimble
 3. The apparatus of claim 1, wherein the ram controlsystem is a hydraulic system.
 4. The apparatus of claim 3 furtherincluding a plurality of hydraulic circuits, each hydraulic circuitbeing operatively associated with one of the rams to drive the ram. 5.The apparatus of claim 4, wherein each hydraulic circuit includes apiston-cylinder arrangement for driving the ram associated with thehydraulic circuit.
 6. The apparatus of claim 5, wherein each hydrauliccircuit includes a pump operatively connected to the piston-cylinderarrangement of the circuit.
 7. The apparatus of claim 6, wherein thepumps have the same displacement and are arranged in tandem with a motorto synchronize the movement of the piston-cylinder arrangements.
 8. Theapparatus of claim 5, where n each hydraulic circuit includes a pressurereducing valve, wherein the pressure reducing valve limits the pressureof the circuit to a preset maximum pressure when the ram control systemis in the first mode, thereby limiting the force applied by the ramagainst the stub is limited to the preset maximum force.
 9. Theapparatus of claim 8, wherein each hydraulic circuit includes a pressuresensor, wherein the ram control system enters the second mode when thepressure sensor of each hydraulic circuit indicates that the pressure ofthe hydraulic circuit has reached the preset maximum pressure.
 10. Theapparatus of claim 9, wherein the pressure of each hydraulic circuit isnot limited to the preset maximum pressure when the ram control systemis in the second mode.
 11. A method for removing thimbles from stubs ofan anode, the method comprising: advancing a ram towards each stub,while limiting the force applied by the ram against the stub to a presetmaximum force; and advancing the rams at the same speed to push thestubs through the thimbles, while not limiting the force applied by eachram to the preset maximum force.
 12. The method of claim 11, whereinstarting advancing the rams at the same speed after the forces appliedby the rams against the stubs reach the preset maximum forces.
 13. Themethod of claim 11 further including holding at least one of thethimbles stationary while advancing the rams at the same speed to pushthe stubs through the thimbles.
 14. The method of claim 11, whereinadvancing a ram towards each stub includes advancing the ram towards thestub using a hydraulic circuit that includes a piston-cylinderarrangement and a pump operatively connected to the piston-cylinderarrangement.
 15. The method of claim 14, wherein limiting the forceapplied by the ram against the end to the preset maximum force includeslimiting the pressure of the hydraulic circuit to a preset maximumpressure.
 16. The method of claim 15, wherein advancing the rams at thesame speed includes providing the pumps with the same displacement anddriving the pumps in tandem.